Laser apparatus, laser annealing method, and manufacturing method of a semiconductor device

ABSTRACT

To provide a laser apparatus and a laser annealing method with which a crystalline semiconductor film with a larger crystal grain size is obtained and which are low in their running cost. A solid state laser easy to maintenance and high in durability is used as a laser, and laser light emitted therefrom is linearized to increase the throughput and to reduce the production cost as a whole. Further, both the front side and the back side of an amorphous semiconductor film is irradiated with such laser light to obtain the crystalline semiconductor film with a larger crystal grain size.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of annealing a semiconductorfilm with the use of laser light (hereinafter referred to as laserannealing) and to a laser apparatus for performing the laser annealing(an apparatus including a laser and an optical system for leading laserlight output from the laser to a process object). The invention alsorelates to a semiconductor device fabricated by a manufacturing processthat comprises the laser annealing step, and to the manufacturingprocess. The semiconductor device here includes an electro-opticaldevice such as a liquid crystal display device and an EL display device,and an electronic device having the electro-optical device as one of itscomponents.

2. Description of the Related Art

An advance has been made in recent years in development of thin filmtransistors (hereinafter referred to as TFTs), and TFTs usingpolycrystalline silicon films (polysilicon films) as crystallinesemiconductor films are receiving the attention. In liquid crystaldisplay devices (liquid crystal displays) and EL (electroluminescence)display devices (EL displays), in particular, such TFTs are used aselements for switching pixels and elements for forming driver circuitsto control the pixels.

General means for obtaining a polysilicon film is a technique in whichan amorphous silicon film is crystallized into a polysilicon film. Amethod in which an amorphous silicon film is crystallized with the useof laser light has lately become the one that is especially notable. Inthis specification, to crystallize an amorphous semiconductor film withlaser light to obtain a crystalline semiconductor film is called lasercrystallization.

The laser crystallization is capable of instantaneous heating ofsemiconductor film, and hence is an effective technique as measures forannealing a semiconductor film formed on a low heat resistant substratesuch as a glass substrate or a plastic substrate. In addition, the laserannealing makes the throughput definitely higher as compared withconventional heating measures using an electric furnace (hereinafterreferred to as furnace annealing).

There are various kinds of laser light, of which the general one to beused in laser crystallization is laser light generated and emitted froma pulse oscillation type excimer laser as a source (hereinafter referredto as excimer laser light). The excimer laser has advantages in that itis large in output and that it is capable of repetitive irradiation at ahigh frequency and, moreover, excimer laser light is advantageous interms of its high absorption coefficient with respect to silicon films.

To generate excimer laser light, KrF (wavelength, 248 nm) or XeCl(wavelength, 308 nm) is used as an excitation gas. However, Kr (krypton)gas and Xe (xenon) gas are very expensive, causing a problem of increasein production cost when recharge of the gas is frequent.

In addition, every two or three years, excimer laser annealing requiresreplacement of attachments such as a laser tube for laser oscillationand a gas refinery for removing unnecessary compounds that are producedduring the course of oscillation. Many of these attachments are alsoexpensive, taking part in increasing the production cost.

As seen in the above, a laser apparatus using excimer laser light doespossess high ability but also possess drawbacks in that maintenancethereof is very troublesome and that the running cost (which means thecosts required for operating the apparatus) is high for a laserapparatus for mass production.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is therefore to provide a laser apparatus whichis capable of providing a crystalline semiconductor film with a largercrystal grain size than in prior art and which is low in running cost,and to provide a laser annealing method using that laser apparatus.Another aspect of the present invention is to provide a semiconductordevice fabricated by using the laser annealing method and a method ofmanufacturing the semiconductor device.

The present invention is characterized in that the front side and theback side of a semiconductor film are irradiated with laser lightgenerated and emitted from a solid state laser (a laser that outputslaser light using a crystal rod as a resonance cavity) as a source.

When the semiconductor film is irradiated, the laser light is preferablylinearized by an optical system. To linearize laser light indicates thatlaser is formed into such a shape as to make the irradiated area linearwhen a process object is irradiated with the laser light. In short, itindicates that the sectional shape of the laser light is linearized. Theterm “linear” here does not mean a line in the strict sense of the word,but means a rectangle (or an oblong) with a large aspect ratio. Forinstance, a rectangle or an oblong having an aspect ratio of 10 or more(preferably 100 to 10000).

In the above construction, the solid state laser may be generally knownones such as a YAG laser (which usually indicates an Nd:YAG laser), anNd:YVO₄ laser, an Nd:YAIO₃ laser, a ruby laser, a Ti:sapphire laser, ora glass laser. The YAG laser is particularly preferable because of itssuperiority in coherence and pulse energy. There are a continuous waveYAG laser and a pulse oscillation type YAG laser and the latter isdesirable in the present invention, for it is capable of large areairradiation.

However, the fundamental wave (a first harmonic) of the YAG laser has ashigh wavelength as 1064 nm. It is therefore preferable to use secondharmonic (wavelength, 532 nm), third harmonic (wavelength, 355 nm), orfourth harmonic (wavelength, 266 nm).

In particular, the second harmonic of the YAG laser has a frequency of532 nm and is within a wavelength range (around 530 nm) in whichreflection at an amorphous silicon film is the least when the amorphoussilicon film is irradiated with the second YAG laser wave. In thiswavelength range, in addition, the quantity of transmittable laser lightthrough the amorphous semiconductor film is enough to efficientlyirradiate again the amorphous semiconductor film from its back sideusing a reflective member. Moreover, the laser energy of the secondharmonic is large, about 1.5 J/pulse at a maximum (in an existing pulseoscillation type YAG laser apparatus). When it is linearized, the lengththereof in the longitudinal direction is therefore markedly lengthenedto make it possible to irradiate a large area at once with laser light.These harmonics can be obtained by using a non-linear crystal.

The fundamental wave can be modulated into the second harmonic the thirdharmonic, or the fourth harmonic by a wavelength modulator that includesa non-linear element. The respective harmonics may be formed byfollowing any known technique. In this specification, “laser lightgenerated and emitted from a solid state laser as a source” includes notonly the fundamental wave but also the second harmonic, the thirdharmonic, and the fourth harmonic which are obtained by modulating thewavelength of the fundamental wave.

Alternatively, the Q switch method (Q modulation switch method) that isoften used in the YAG laser may be employed. This method is tosufficiently lower the Q value of a laser resonator in advance and tothen rapidly raise the Q value, to thereby output sharp pulse laserhaving a very high energy value. The method is one of known techniques.

The solid state laser used in the present invention can output laserlight as long as a solid crystal, a resonant mirror, and a light sourcefor exciting the solid crystal are satisfied, basically. Therefore,maintenance thereof is not laborious unlike the excimer laser. In otherwords, the running cost of the solid state laser is significantly lessas compared with the excimer laser, making it possible to greatly reducethe production cost of a semiconductor device. A decrease in number ofthe maintenance leads to an increase of the operating rate of themass-production line, so that the throughput along the manufacturingsteps is improved as a whole. This also contributes considerably to thereduction in production cost of the semiconductor device. Moreover, thesolid state laser occupies a smaller area than the excimer laser does,which is advantageous in designing a production line.

In addition, to perform laser annealing by irradiating the front sideand the back side of an amorphous semiconductor film with laser lightallows obtainment of a crystalline semiconductor film with a largercrystal grain size than in prior art (where the amorphous semiconductorfilm is irradiated with laser light only from its front side). Accordingto the applicant of the present invention, it is considered thatirradiation of laser light onto the front side and the back side of anamorphous semiconductor film slows down the cycle of fusion andsolidification of the semiconductor film, and that the crystal grainsize is increased as a result.

The obtainment of a crystalline semiconductor film with a large crystalgrain size leads to a considerable improvement of the performance of thesemiconductor device. Taking a TFT as an example, enlargement of acrystal grain size allows reduction in number of crystal grainboundaries that may be contained in a channel formation region. That is,it allows fabricating a TFT that has one, preferably zero, crystal grainboundary in its channel formation region. Since the crystallinity ofeach crystal grain is such that it may substantially be regarded as asingle crystal, to obtain a mobility (electric field effect mobility)equal to or higher than that of a transistor using a single crystalsemiconductor is also possible.

Further, carriers cross the crystal grain boundaries extremely lessfrequently in the present invention to thereby reduce the fluctuation ofON current values (drain current when a TFT is in ON state), OFF currentvalues (drain current when a TFT is in OFF state), threshold voltage, ofS values, and electric field effect mobility.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams showing the structure of a laser apparatus;

FIGS. 2A and 2B are diagrams showing the structure of an optical systemof a laser apparatus;

FIG. 3 is a diagram illustrating a laser annealing method of the presentinvention;

FIGS. 4A and 4B are diagrams showing the structure of a laser apparatus;

FIG. 5 is a diagram illustrating a laser annealing method of the presentinvention;

FIG. 6 is a diagram illustrating a laser annealing method of the presentinvention;

FIGS. 7A to 7E are diagrams showing a process of manufacturing an activematrix substrate;

FIGS. 8A to 8D are diagrams showing a process of manufacturing an activematrix substrate;

FIGS. 9A to 9C are diagrams showing a process of manufacturing an activematrix substrate;

FIGS. 10A to 10E are diagrams showing a process of manufacturing anactive matrix substrate;

FIGS. 11A to 11E are diagrams showing a process of manufacturing anactive matrix substrate;

FIG. 12 is a diagram showing a pixel structure;

FIGS. 13A and 13B are diagrams showing the sectional structure of anactive matrix type liquid crystal display device;

FIG. 14 is a diagram showing the top structure of an active matrix typeliquid crystal display device;

FIG. 15 is a perspective view showing an active matrix type liquidcrystal display device;

FIGS. 16A to 16F are diagrams showing examples of an electronic device;

FIGS. 17A to 17D are diagrams showing examples of a projector; and

FIG. 18 is a diagram illustrating a laser annealing method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment Mode 1

An embodiment mode of the present invention will be described. FIG. 1Ais a diagram showing the structure of an laser apparatus including alaser of the present invention. This laser apparatus has an Nd:YAG laser101, an optical system 201 for linearizing laser light (preferablysecond harmonic, third harmonic, or fourth harmonic) generated andemitted from an Nd:YAG laser 101, and a stage 102 on which a lighttransmittable substrate is fixed. The stage 102 is provided with aheater 103 and a heater controller 104 to heat the substrate up to atemperature of 100 to 450° C. A reflective member 105 is provided on thestage 102, and placed on the reflective member 105 is a substrate 106 onwhich an amorphous semiconductor film is formed.

If the laser light output from the Nd:YAG laser 101 is modulated intoany of the second to fourth harmonics, a wavelength modulator includinga non-linear element is set right behind the Nd:YAG laser 101.

Next will be described, with reference to FIG. 1B, how to hold thesubstrate 106 in the laser apparatus having the structure as shown inFIG. 1A. The substrate 106 held by the stage 102 is set in a reactionchamber 107, and irradiated with linear laser light generated andemitted from the laser 101 as a source. The inside of the reactionchamber may be decompressed by an exhaust system (not shown), or mayhave an inert gas atmosphere by using a gas system (not shown), so thatthe semiconductor film can be heated up to a temperature of 100 to 450°C. without contaminating the film.

The stage 102 can be moved along a guide rail 108 within the reactionchamber, making it possible to irradiate the entire surface of thesubstrate with laser light. The laser light enters from a not-shownwindow that is formed from quarts on the top surface of the substrate106. In FIG. 1B, a transfer chamber 109, an intermediate chamber 110,and a loading/unloading chamber 111 are connected to the reactionchamber 107, and these chambers are separated from each other by gatevalves 112, 113.

A cassette 114 that is capable of holding a plurality of substrates isplaced in the loading/unloading chamber 111. The substrates aretransported by a transporting robot 115 that is installed in thetransfer chamber 109. Reference symbol 106′ denotes a substrate in thetransportation. With such a structure, successive laser annealing can becarried out under reduced pressure or in an inert gas atmosphere.

Next, the structure of the optical system 201 for linearizing laserlight will be described with reference to FIGS. 2A and 2B. FIG. 2A is aview of the optical system 201 viewed from its side, and FIG. 2B is aview of the optical system 201 viewed from its top.

The laser light generated and emitted from the laser 101 as a source issplit longitudinally by a cylindrical lens array 202. The split laserlight is further split laterally by a cylindrical lens array 203. Thatis, ultimately, the laser light is split by the cylindrical lens arrays202, 203 into matrix.

Then the laser light is condensed once by a cylindrical lens 204. Thelaser light passes through a cylindrical lens 205 right after thecylindrical lens 204. Thereafter, the laser light is reflected at amirror 206, passes through a cylindrical lens 207, and then reaches anirradiated area 208.

At this point, the laser light projected onto the irradiated area 208 islinear. This means that the sectional shape of the laser lighttransmitted through the cylindrical lens 207 is linear. The linearizedlaser light is homogenized in its width direction (shorter one) by thecylindrical lens array 202, the cylindrical lens 204, and thecylindrical lens 207. On the other hand, the linearized laser light ishomogenized in its length direction (longer one) by the cylindrical lensarray 203 and the cylindrical lens 205.

A description given next with reference to FIG. 3 is about anarrangement for irradiating the process film formed on the substratefrom its front and back with the laser light. FIG. 3 is a diagramshowing the positional relation between the substrate 106 and thereflective member 105 in FIG. 1A.

In FIG. 3, reference symbol 301 denotes a light transmittable substrate,the front side (the side where a thin film or an element is to beformed) of which has an insulating film 302 and an amorphoussemiconductor film (or a microcrystal semiconductor film) 303 formedthereon. A reflective member 304 for reflecting laser light is arrangedbeneath the light transmittable substrate 301.

The light transmittable substrate 301 may be a glass substrate, a quartzsubstrate, a crystallized glass substrate or a plastic substrate. Forthe insulating film 302, an insulating film containing silicon, such asa silicon oxide film or a silicon oxide nitride film (SiOxNy) film, maybe used. Prospective films for the amorphous semiconductor film 303include an amorphous silicon film, an amorphous silicon germanium film,etc.

A metal film formed on a surface (where the laser light is to bereflected) of a substrate may be used as the reflective member 304.Alternatively, a substrate formed of a metal element may serve as thereflective member 304. In that case, any material may be used for themetal film. Typically used is a metal film containing any element chosenout of aluminum, silver, tungsten, titanium, and tantalum.

It is also possible to directly form a metal film as above on the backside of the substrate 301, instead of arranging the reflective member304, so that the laser light is reflected at the metal film. Note thatthis structure is possible only when the metal film formed on the backside is not removed during the manufacture of a semiconductor device.

The amorphous semiconductor film 303 is then irradiated with the laserlight that has been linearized through the optical system 201 (only thecylindrical lens 207 is shown in the drawing) illustrated in FIGS. 2Aand 2B.

At this point, the amorphous semiconductor film 303 is irradiated withtwo beams of laser light, i.e., laser light 305 that passes through thecylindrical lens 207 to directly irradiate the film, and laser light 306that is reflected at the reflective member 304 before it irradiates theamorphous semiconductor film 303. In this specification, the laser lightused to irradiate the front side of the amorphous semiconductor film iscalled a primary laser light while the laser light used to irradiate theback side thereof is called a secondary laser light.

The laser light passes through the cylindrical lens 207 to have an angleof incident of 45 to 90° with respect to the front side of the substrateduring the process of being condensed. For that reason, the secondarylaser light 306 is the light that reaches further to the back side ofthe amorphous semiconductor film 303 so as to irradiate there. Thesecondary laser light 306 may be obtained more efficiently by forming anuneven portion on the reflective surface of the reflective member 304 todiffuse the laser light.

In particular, the second harmonic of the YAG laser has a frequency of532 nm and is within a wavelength range (around 530 nm) in whichreflection at an amorphous semiconductor film is the least when theamorphous semiconductor film is irradiated with the second YAG laserwave. In this wavelength range, in addition, the quantity oftransmittable laser light through the amorphous semiconductor film isenough to efficiently irradiate again the amorphous semiconductor filmfrom its back side using the reflective member. Moreover, the laserenergy of the second harmonic is large, about 1.5 J/pulse at a maximum(in an existing pulse oscillation type YAG laser apparatus). When it islinearized, the length thereof in the longitudinal direction istherefore markedly lengthened to make it possible to irradiate a largearea at once with laser light.

As described above, according to this embodiment mode, the laser lightgenerated and emitted from the solid state laser as a source can belinearized, and the linearized laser light can be split into the primarylaser light and the secondary laser light in the optical system so as tobe used to irradiate the front side of the amorphous semiconductor filmand the back side thereof, respectively.

Embodiment Mode 2

A description given here is a different mode for carrying out thepresent invention from Embodiment Mode 1. This embodiment mode shows anexample in which, without using a reflecting member as described inEmbodiment Mode 1, an amorphous semiconductor film is irradiated fromits front and back with laser light split into two strains of laserlight by some constituent of an optical system.

FIG. 4A is a diagram showing the structure of a laser apparatusincluding a laser of this embodiment mode. The structure is basicallythe same as that of the laser apparatus described in Embodiment Mode 1with FIGS. 1A and 1B. Accordingly, only parts different from the ones inthe precedent mode are given different symbols and are explained.

This laser apparatus has an Nd:YAG laser 101, an optical system 401 forlinearizing laser light that is generated and emitted from an Nd:YAGlaser 101 and splitting into two strains laser light (preferably thirdharmonic, or fourth harmonic), and a light transmittable stage 402 onwhich a light transmittable substrate is fixed. A substrate 403 a is seton the stage 402, and an amorphous semiconductor film 403 b is formed onthe substrate 403 a.

If the laser light output from the Nd:YAG laser 101 is modulated intoeither the third harmonic or the fourth harmonic, a wavelength modulatorincluding a non-linear element is set right behind the Nd:YAG laser 101.

In the case of this embodiment mode, the amorphous semiconductor film403 b is irradiated with laser light that has been transmitted throughthe stage 402, and hence the stage 402 has to be light transmittable. Itis desirable to suppress as much attenuation as possible at the stage402, because the energy of the laser light irradiated from the stage 402(a secondary laser light) is expectedly attenuated when the laser lightis transmitted through the substrate.

FIG. 4B is a diagram illustrating how to hold the substrate 403 a in thelaser apparatus shown in FIG. 4A. The explanation thereof is omitted,however, for the arrangement thereof is the same as the one shown inFIG. 1B except that the light transmittable stage 402 is used here.

Next, the structure of the optical system 401 shown in FIG. 4A will bedescribed with reference to FIG. 5. FIG. 5 is a view of the opticalsystem 401 viewed from its side. Laser light generated and emitted froman Nd:YAG laser 501 as a source (the third harmonic or the fourthharmonic) is split longitudinally by a cylindrical lens array 502. Thesplit laser light is further split laterally by a cylindrical lens array503. The laser light is thus split by the cylindrical lens arrays 502,503 into matrix.

Then the laser light is condensed once by a cylindrical lens 504. Thelaser light passes through a cylindrical lens 505 right after thecylindrical lens 504. The optical system 401 is the same as the oneshown in FIGS. 2A and 2B up through this point.

Thereafter, the laser light enters into a half mirror 506 and is splithere into a primary laser light 507 and a secondary laser light 508. Theprimary laser light 507 is reflected at mirrors 509, 510, passes througha cylindrical lens 511, and then reaches the front side of the amorphoussemiconductor film 403 b.

The secondary laser light 508 split by the half mirror 506 is reflectedat mirrors 512, 513, 514, passes through a cylindrical lens 515, andthen transmits through the substrate 403 a to reach the back side of theamorphous semiconductor film 403 b.

At this point, the laser light projected onto an irradiated area on thesubstrate is linear as in Embodiment Mode 1. The linearized laser lightis homogenized in its width direction (shorter one) by the cylindricallens array 502, the cylindrical lens 504, and the cylindrical lens 515.On the other hand, the linearized laser light is homogenized in itslength direction (longer one) by the cylindrical lens array 503, thecylindrical lens 505, and the cylindrical lens 509.

As described above, according to this embodiment mode, the laser lightgenerated and emitted from the solid state laser as a source can belinearized, and the linearized laser light can be split into the primarylaser light and the secondary laser light so as to be used to irradiatethe front side of the amorphous semiconductor film and the back sidethereof, respectively.

Embodiment Mode 3

A description given here is about an embodiment mode different fromEmbodiment Mode 2. This embodiment mode shows an example in which laserlight is split into two strains of laser light by some constituent of anoptical system, the two laser beams are made into a third harmonic and afourth harmonic, respectively, and laser annealing of an amorphoussemiconductor film is carried out by irradiating its front with thefourth harmonic while irradiating its back with the third harmonic.

FIG. 6 is a side view of the optical system of a laser apparatus for usein this embodiment mode. The laser light generated and emitted from anNd:YAG laser 601 as a source is split by a half mirror 602. Note that,though not shown, a part of a fundamental wave output from the Nd:YAGlaser 601 is modulated into a third harmonic having a wavelength of 355nm before reaching the half mirror 602.

First, laser light which has transmitted through the half mirror 602 (toserve as a secondary laser light) travels through cylindrical lensarrays 603, 604, cylindrical lenses 605, 606, a mirror 607, acylindrical lens 608, and a substrate 609 a to be used to irradiate theback side of an amorphous semiconductor film 609 b.

The laser light used ultimately to irradiate the back side of anamorphous semiconductor film 609 b is linearized. The process oflinearization is the same as in the explanation of the optical system ofFIGS. 2A and 2B, and hence is not described here.

Laser light which has been reflected at the half mirror 602 (to serve asa primary laser light) is modulated into a fourth harmonic having awavelength of 266 nm by a wavelength modulator 610 that includes anon-linear element. Thereafter, the laser light travels through a mirror611, cylindrical lens arrays 612, 613, cylindrical lenses 614, 615, amirror 616, and a cylindrical lens 617 to be used to irradiate the frontside of the amorphous semiconductor film 609 b.

The laser light used ultimately to irradiate the back side of anamorphous semiconductor film 609 b is linearized. The process oflinearization is the same as in the explanation of the optical system ofFIGS. 2A and 2B, and hence is not described here.

As described above, this embodiment mode is characterized in that thefront side of the amorphous semiconductor film is irradiated with thefourth harmonic with a wavelength of 266 nm while the back side of theamorphous semiconductor film is irradiated with the third harmonic witha wavelength of 355 nm. It is preferable to linearize the sectionalshape of the third harmonic and the fourth harmonic as in thisembodiment mode, for the throughput of the laser annealing is improved.

When the substrate 609 a is a glass substrate, light with a wavelengthshorter than 250 nm or so does not transmit through the substrate. Asfor the #1737 substrate with a thickness of 1.1 mm, a product ofCorning, Ltd., light with a wavelength of about 240 nm is the first thatcan transmit the substrate. The substrate allows about 38% of light witha wavelength of 300 nm to transmit therethrough, about 85% if it is 350nm, and about 90% if it is 400 nm. That is, to use laser light with awavelength of 350 nm or more (preferably with 400 nm or more wavelength)as the secondary laser light is desirable when a glass substrate isemployed for the substrate 609 a.

Accordingly, when an Nd:YAG laser is used for a solid state laser and aglass substrate is used for the substrate on which the amorphoussemiconductor film is formed as in this embodiment mode, it is desirableto make the primary laser light that does not transmit the substrateinto the fourth harmonic and to make the secondary laser light thattransmits the substrate into the third harmonic.

As described above, it is effective to adopt a different wavelength ofthe laser light used to irradiate the front side of the amorphoussemiconductor film (the primary laser light) from a wavelength of thelaser light used to irradiate the back side of the amorphoussemiconductor film (the secondary laser light), in accordance with thematerial of the substrate or the film quality of the amorphoussemiconductor film.

Although used in this embodiment mode is split laser light which hasbeen generated and emitted from one laser as a source, two lasers thatoutput laser light of different wavelengths may alternatively be used.

Embodiment 1

An embodiment of the present invention is described by using FIGS. 7A to9C. A method for manufacturing a pixel TFT and a storage capacitor ofthe pixel section, and an n-channel TFT and a p-channel TFT of thedriver circuit disposed in the periphery of the pixel section, at thesame time, is described here.

In FIG. 7A, barium borosilicate glass or aluminoborosilicate glass astypified by Corning #7059 glass and #1737 glass can be used for asubstrate 701. Besides these glass substrates, plastic substrates nothaving optical anisotropy such as polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyethersulfone (PES), etc. can also beused.

A base film 702 comprising such as a silicon oxide film, a siliconnitride film or a silicon oxynitride film is formed over the surface ofthe substrate 701, on which TFT is to be formed, in order to prevent thediffusion of impurities from the substrate 701. For example, a laminateof the silicon oxynitride film 702 a formed from SiH₄, NH₃ and N₂O byplasma CVD to a thickness of 10 to 200 nm (preferably, 50 to 100 nm) anda hydrogenated silicon oxynitride film 702 b formed similarly from SiH₄and N₂O to a thickness of 50 to 200 nm (preferably, 100 to 150 nm), isformed.

The silicon oxynitride film is formed by using the conventional parallelplate type plasma-enhanced CVD. The silicon oxynitride film 702 a isformed by introducing SiH, at 10 sccm, NH₃ at 100 sccm and N₂O at 20sccm into a reaction chamber under the condition of a substratetemperature of 325° C., a reaction pressure of 40 Pa, a discharge powerdensity of 0.41 W/cm² and a discharge frequency of 60 MHZ. On the otherhand, hydrogenated silicon oxynitride film 702 b is formed byintroducing SiH₄ at 5 sccm, N₂O at 120 sccm and H₂ at 125 sccm into areaction chamber under the condition of the substrate temperature 400°C., a reaction pressure of 20 Pa, a discharge power density of 0.41W/cm² and a discharge frequency of 60 MHZ. These films can be formedsuccessively by only changing the substrate temperature and by switchingthe reactive gases.

Further, the silicon oxynitride film 702 a is formed so that itsinternal stress is a pulling stress when considering the substrate asthe center. The silicon oxynitride film 702 b is made to have itsinternal stress in the similar direction but it is made to have asmaller stress in the absolute value, compared with that of the siliconoxynitride film 702 a.

Next, an amorphous semiconductor film 703 having a thickness of 25 to 80nm (preferably, 30 to 60 nm) and an amorphous structure is formed by aknown method such as plasma CVD or sputtering. For example, an amorphoussilicon film is formed to a thickness of 55 nm by plasma CVD. Both thebase film 702 and the amorphous semiconductor film 703 can be formedcontinuously. For example, after the silicon oxynitride film 702 a andthe hydrogenated silicon oxynitride film 702 b are formed continuouslyby the plasma CVD as described above, the deposition can be carried outcontinuously by switching the reactive gases from SiH₄, N₂O and H₂ toSiH₄ and H₂, or SiH₄ alone, without exposing to the atmosphere of theopen air. As a result, the contamination of the surface of thehydrogenated silicon oxynitride film 702 b can be prevented, andvariance of the characteristics of the TFT to be fabricated andfluctuation of the threshold voltage can be reduced.

Island semiconductor layers 704 to 708 are then formed into the firstshape as shown by dotted line in FIG. 7B, from the semiconductor layer703 which has an amorphous structure. FIG. 10A is a top view of islandsemiconductor layers 704 and 705 of this state and FIG. 11A similarlyshows a top view of an island semiconductor layer 708.

In FIGS. 10 and 11 the island semiconductor layers are formed intorectangles of each side at 50 μm or less however it is possible to formthe shape of the island semiconductor layers arbitrarily, preferablyprovided that the minimum distance from its center to the edge is 50 μmor less it may can be any polygon or circular shape.

Next crystallization process is performed onto such island semiconductorlayers 704 to 708. It is possible to use any method described inEmbodiment Modes 1 to 3 for the crystallization process, and laseranneal is performed onto the island semiconductor layers 704 to 708 bythe method of Embodiment Mode 1 in this Embodiment. Island semiconductorlayers 709 to 713 are thus formed from crystalline silicon film as shownby the solid line in FIG. 7B.

Note that though the present Embodiment shows an example of forming oneisland semiconductor layer corresponding to one TFT, it is possible tomake a plural numbers of TFTs connected in series function as one TFT bypartitioning one island semiconductor layers into plural numbers, incase that the surface area exclusively used by an island semiconductorlayer is large (in case that one TFT becomes large).

In this case the film becomes dense as the amorphous silicon filmcrystallizes and it shrinks by about 1 to 15%. A region 714 is formed inthe edge portion of the island semiconductor layer in which strain isgenerated due to the shrinkage. Further, an island semiconductor layercomprising such crystalline silicon film has a pulling stress byconsidering the substrate as its center. FIGS. 10B and 11B respectivelyshows a top view of island semiconductor layers 709, 710 and 713 of thisstate. The regions 704, 705 and 708 shown by dotted line in the samefigures show the size of the island semiconductor layers 704, 705 and708 that existed from the first.

When a gate electrode of a TFT is formed overlapping the region 714 inwhich such strain is accumulated, it becomes a cause for degrading theTFT characteristics since there are a number of defect levels and thecrystallinity is no good. OFF current value increases or heat isgenerated regionally because current is concentrated into this region,for instance.

Accordingly as shown in FIG. 7C, island semiconductor layers 715 to 719of the second shape are formed so as to remove the region 714 in whichsuch strain is accumulated. The region 714′ shown by a dotted line inthe figure is an area where the region 714 in which strain isaccumulated existed, and the figure shows the condition in which islandsemiconductor layers 715 to 719 of the second shape are formed insidesuch area. The shape of the island semiconductor layers 715 to 719 ofthe second shape may be set arbitrarily. FIG. 10C shows a top view ofthe island semiconductor layers 715 and 714 of this state. Further, FIG.11C shows a top view of the island semiconductor layer 719.

Thereafter a mask layer 720 is formed from silicon oxide film into 50 to100 nm by plasma CVD or sputtering, so as to cover the islandsemiconductor layers 715 to 719. An impurity element which impartsp-type may be added onto the entire surface of the island semiconductorlayers of this state to a concentration from 1×10¹⁶ to 5×10¹⁷ atoms/cm³for the purpose of controlling the threshold voltage of the TFTs (VT).

The elements of the Group XIII of the Periodic Table such as boron (B),aluminum (Al) or gallium (Ga) are known as the impurity elements forimparting p-type to the semiconductor. Ion implantation or ion dopingcan be adopted as the method of doping these elements, but ion doping issuitable for processing a substrate having a large area. This ion dopingmethod uses diborane (B₂H₆) as a source gas and adds boron (B). Additionof such an impurity element is not always necessary and may be omitted.However, this is the method that can be used appropriately for keepingthe threshold voltage of the n-channel TFT, in particular, within aprescribed range.

In order to form an LDD region in the n-channel TFT in the drivercircuit, an impurity element for imparting the n type is selectivelyadded into island semiconductor layers 716 and 718. Resist masks 721 ato 721 e are formed in advance for this purpose. As an impurity elementwhich imparts n-type, phosphorus (P) or arsenic (As) may be used and iondoping using phosphine (PH₃) is used here for adding phosphorus (P).

The concentration of phosphorus (P) in the formed impurity regions maybe within the range of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ as the lowconcentration n-type impurity regions 722 and 723. Through thespecification the concentration of the impurity element which impartsn-type contained in the impurity regions 722 and 723 formed here isdenoted as (n⁻). Further, the impurity region 724 is a semiconductorlayer for forming a storage capacitor of the pixel section andphosphorus (P) is added in this region as well in the sameconcentration. (FIG. 7D)

A step for activating the added impurity element is performed next. Theactivation can be performed by heat treatment in a nitrogen atmosphereat 500 to 600° C. for 1 to 4 hours or laser activation. Further, the twomay be performed in combination. In case of adopting laser activation,KrF excimer laser light (wavelength 248 nm) is used, a linear beam isformed under the condition of oscillation frequency 5 to 50 Hz andenergy density at 100 to 500 mJ/cm², and the beam is scanned with theoverlap ratio of the linear beam to 80 to 98% to treat the entiresurface of the substrate on which island semiconductor layers areformed. Note that there is no item that limits the laser lightirradiation conditions and they may be appropriately determined by theoperator. This process may be performed with the mask layer 720remained, or it may be performed after removal.

In FIG. 7E, the gate insulating film 725 is formed from an insulatingfilm containing silicon to a thickness between 40 and 150 nm by usingplasma CVD or sputtering. For example, it may be formed from a siliconoxynitride film to 120 nm thickness. Further, the silicon oxynitrodefilm manufactured by adding O₂ to SiH₄ and N₂O has a reduced fixedelectric charge density in the film and therefore is a preferablematerial for this use. Needless to say, the gate insulating film 725 isnot limited to such silicon oxynitride film, and it may use a singlelayer or a laminate structure of other insulating films containingsilicon. In any case, the gate insulating film 725 is formed so as to bea compressing stress by considering the substrate as its center.

A heat resistant conductive layer is formed as shown in FIG. 7E to forma gate electrode on the gate insulating film 725. The heat resistantconductive film may comprise a single layer, but may be a laminatestructure of plurality of layers such as double layer or triple layer,if necessary. By using such heat resistant conductive materials, thestructure in which the conductive layer (A) 726 comprising a conductivemetal nitride film and the conductive layer (B) 727 which comprises ametal film are laminated may be formed for example.

The conductive layer (B) 727 may be formed from an element selected fromtantalum (Ta), titanium (Ti), molybdenum (Mo) and tungsten (W), or analloy film comprising mainly of these elements or an alloy filmcombining the above elements (typically, a Mo—W alloy film, an Mo—Taalloy film), and the conductive layer (A) 726 may be formed fromtantalum nitride (TaN), tungsten nitride (WN), titanium nitride (TiN),molybdenum nitride (MoN), etc. The conductive layer (A) 726 may adopttungsten silicide, titanium silicide or molybdenum suicide.

The impurity concentration contained in the conductive layer (B) 727 maybe preferably reduced for low resistance, specifically the oxygenconcentration may be reduced to 30 ppm or below. For example,resistivity of 20 μΩcm or below can be realized with respect to tungsten(W) by setting the oxygen concentration at 30 ppm or below.

The conductive layer (A) 726 may be formed to 10 to 50 nm (preferably 20to 30 nm) and the conductive layer (B) 727 may be formed to 200 to 400nm (preferably 250 to 350 nm). In the case of using W for the gateelectrode, tungsten nitride (WN) is formed to a thickness of 50 nm forthe conductive layer (A) 726 by sputtering using W as a target and byintroducing an argon (Ar) gas and a nitrogen (N₂) gas, and W is formedto a thickness of 250 nm for the conductive layer (B) 727. As anothermethod, W film can be formed by thermal CVD using tungsten hexafluoride(WF₆).

In any case, it is necessary to devise low resistivity for using as agate electrode, and the resistivity of the W film is preferably nothigher than 20 μΩcm. The low resistivity of the W film can beaccomplished by increasing the crystal grain size, but the resistivitybecomes high when the contents of the impurity elements such as oxygenin W are great because crystallization is impeded. Therefore, whensputtering is employed, the W target used has a purity of 99.9999%, andsufficient attention should be paid lest impurities mix from the gaseousphase during the formation of the film. In this way, the resistivity of9 to 20 μΩcm can be achieved.

On the other hand, in case of using TaN film for the conductive layer(A) 726 and Ta film for the conductive layer (B) 727, it is possible toform similarly by sputtering. TaN film is formed by using Ta as thetarget and the mixed gas of Ar and nitrogen for the sputtering gas, andargon (Ar) is used as the sputtering gas to form the Ta film. When asuitable amount of Xe or Kr is added to the sputtering gas, the internalstress of the resulting films can be mitigated and peel of the films canbe prevented. The resistivity of the a phase Ta film is about 20 μΩcm,and this film can be used for the gate electrode. However, theresistivity of the β phase Ta film is about 180 μΩcm and this film isnot suitable for the gate electrode. The TaN film has a crystalstructure approximate to that of the a phase. Therefore, when the Tafilm is formed on the TaN film, the a phase Ta film can be obtainedeasily.

Incidentally, though not shown in the figure, it is effective to form aphosphorus (P) doped silicon film to a thickness of about 2 to about 20nm under the conductive layer (A) 726. By doing so, the improvement ofadhesiveness and prevention of oxidation of the conductive film formedthereon can be devised and at the same time it is possible to preventthe alkali metal elements contained in the conductive layer (A) 726 orthe conductive layer (B) 727 in a trace amount to diffuse into the gateinsulating film 725. In any case, it is preferable to set theresistivity of the conductive layer (B) 727 within a range between 10and 50 μΩcm.

Next, resist masks 728 a to 728 f are formed by photolithography byusing a photo-mask, and the conductive layer (A) 726 and the conductivelayer (B) 727 are collectively etched to form gate electrodes 729 to 733and a capacitance wiring 734. These gate electrodes 729 to 733 andcapacitance wiring 734 comprise a unitary structure of 729 a to 733 acomprising the conductive layer (A) and 729 b to 733 b comprising theconductive layer (B). (FIG. 8A)

The relations of the arrangement of the island semiconductor layers 715and 716 and gate electrodes 729 and 730 in this state is shown in FIG.10D. Similarly the relations between the island semiconductor layer 719,the gate electrode 733 and the capacitor wiring 734 is shown in FIG.11D. The gate insulating film 725 is omitted from FIGS. 10D and 11D.

Though the method for etching the conductive layer (A) and theconductive layer (B) may be appropriately selected by the operator, itis preferable to adopt dry etching using high density plasma forperforming etching at a high speed and with high precision, in case thatthey are formed from a material which is mainly composed of W asdescribed above. Microwave plasma or inductively coupled plasma (ICP)etching apparatus may be used as a means for obtaining high densityplasma.

For example, in etching of W using an ICP etching apparatus, two kindsof gasses, CF₄ and Cl₂, are introduced into the reaction chamber, thepressure is set at 0.5 to 1.5 Pa (preferably 1 Pa) and high frequency(13.56 MHz) electric power of 200 to 1000W is applied to the inductivecoupling section. At this time, high frequency electric power of 20 W isapplied to the stage on which the substrate is placed, charged tonegative electric potential by its self bias, positive ions areaccelerated and anisotropic etching can be performed. By using ICPetching apparatus, etching speed of 2 to 5 nm/second can be obtainedeven with hard metal films such as W, etc. Further, in order to etchwithout leaving residues, it is good perform over-etching by extendingthe etching time by a proportion of 10 to 20%. However, it is necessaryto pay attention to the selective ratio of etching with the base film.For example, since the selective ratio of the silicon oxynitride film(gate insulating film 725) against W film is 2.5 to 3, the surface wherethe silicon oxynitride film is exposed is etched approximately 20 to 50nm and becomes substantially thin through such over etching treatment.

Thereafter, in order to form LDD region in the n-channel TFT of thepixel TFT, a process of adding an impurity element which imparts n-type(n⁻⁻ doping process) is performed. An impurity element which impartsn-type may be added in a self-aligned manner by ion doping using gateelectrodes 729 to 733 as the mask. The concentration of phosphorus (P)added as the impurity element which imparts n-type is set within aconcentration range between 1×10¹⁶ and 5×10¹⁹ atoms/cm³. In this way,low concentration n-type impurity regions 735 to 739 are formed in theisland semiconductor layers as shown in FIG. 8B.

Formation of high concentration n-type impurity regions which functionas source region or drain region (n⁺ doping process) is performed nextin n-channel TFTs. Resist masks 740 a to 740 d are formed first by usinga photo-mask, and an impurity element imparting n-type is doped to formhigh concentration n-type impurity regions 741 to 746. Phosphorus (P) isused as the impurity element imparting n-type. Ion doping usingphosphine (PH₃) is employed so that the concentration falls within therange of 1×10²⁰ to 1×10²¹ atoms/cm³ (FIG. 8C).

High concentration p-type impurity regions 748 and 749 that function assource region or drain region are formed in the island semiconductorlayers 715 and 717 which form p-channel TFTs. An impurity element whichimparts p-type is added here with the gate electrodes 729 and 731 as themask and high concentration p-type impurity regions are formed in aself-aligning manner. At this time the entire surfaces of the islandsemiconductor films 716, 718 and 719 which form n-channel TFTs arecovered by forming resist masks 747 a to 747 c by using a photo mask.

High concentration p-type impurity regions 748 and 749 are formed by iondoping that uses diborane (B₂H₆). The boron (B) concentration in theregions is 3×10²⁰ to 3×10²¹ atoms/cm³ (FIG. 8D).

Phosphorus (P) is added to the high concentration p-type impurityregions 748 and 749 in a preceding step, in a concentration of 1×10²⁰ to1×10²¹ atoms/cm³ with respect to the high concentration p-type impurityregions 748 a and 749 a, and in a concentration of 1×10¹⁶ to 5×10¹⁹atoms/cm³ with respect to the high concentration p-type impurity regions748 b and 749 b. However, by setting the concentration of boron (B)added in this step to become 1.5 to 3 times higher, no trouble occurs inthe function as the source and drain regions of the p-channel TFT.

Thereafter, as shown in FIG. 9A, a protective insulating film 750 isformed from above the gate electrode and the gate insulating film. Theprotective insulating film may comprise a silicon oxide film, a siliconoxynitride film, a silicon nitride film or a laminate film comprisingthe combination of these films. In any case, the protective insulatingfilm 750 is formed of an inorganic insulating material. The protectiveinsulating film 750 has a film thickness of 100 to 200 nm.

When the silicon oxide film is used, tetraethyl orthosilicate (TEOS) andO₂ are mixed, and the film can be formed by plasma CVD with a reactionpressure of 40 Pa, a substrate temperature of 300 to 400° C. and plasmais discharged at a high frequency (13.56 MHZ) power density of 0.5 to0.8 W/cm². When the silicon oxynitride film is used, the film maycomprise a silicon oxynitride film formed by plasma CVD from SiH₄, N₂Oand NH₃ or a silicon oxynitride film formed from SiH₄ and N₂O. The filmdeposition condition in this case is the reaction pressure of 20 to 200Pa, the substrate temperature of 300 to 400° C., and the high frequency(60 MHZ) power density of 0.1 to 1.0 W/cm². The hydrogenated siliconoxynitride film formed from SiH₄, N₂O and H₂ may be used, as well. Thesilicon nitride film can be formed similarly from SiH₄ and NH₃ by plasmaCVD. The protective insulating film is formed to be a compressing stressby considering the substrate as the center.

Thereafter, the step of activating the impurity elements impartingn-type or p-type added in the respective concentrations is conducted.This step is conducted by a thermal annealing method using a furnaceannealing oven. Besides the thermal annealing method, it is possible toemploy a laser annealing method and a rapid thermal annealing method(RTA method). The thermal annealing method is conducted in a nitrogenatmosphere containing oxygen in a concentration of 1 ppm or below,preferably 0.1 ppm or below, at 400 to 700° C., typically 500 to 600° C.In this embodiment, the heat-treatment is conducted at 550° C. for 4hours. When a plastic substrate having a low heat-resistant temperatureis used for the substrate 101, the laser annealing method is employed(FIG. 9B).

After the activation step, heat-treatment is further conducted in anatmosphere containing 3 to 100% hydrogen at 300 to 450° C. for 1 to 12hours to hydrogenate the island semiconductor layers. This is theprocess step that terminates the dangling bonds in the islandsemiconductor layers by hydrogen that is thermally excited. Plasmahydrogenation (using hydrogen that is excited by plasma) may be used asanother means for hydrogenation. Further if the thermal resistance ofthe substrate 701 permits, island semiconductor layers may behydrogenated by diffusing hydrogen from the hydrogenated siliconoxynitride film 702 b of the base film and the hydrogenated siliconoxynitride film of the protective insulating film 750, by heat treatmentat 300 to 450° C.

After the activation and hydrogenation steps are completed, aninterlayer insulating film 751 made of an organic insulating material isformed to a mean thickness of 1.0 to 2.0 μm. As the organic resinmaterials, polyimide, acrylic, polyamide, polyimidamide, BCB(benzocyclobutene), and so forth can be used. For example, whenpolyimide of the type, that is thermally polymerized after being appliedto the substrate, is used, the material is baked at 300° C. in a cleanoven. When acrylic is used, a two-component type is used. After the mainagent and the curing agent are mixed, the mixture is applied to theentire surface of the substrate by using a spinner. Preparatory heatingis then conducted by using a hot plate at 80° C. for 60 seconds, andbaking is then made in the clean oven at 250° C. for 60 minutes.

By forming the interlayer insulating film from an organic insulatingmaterial, its surface can be planarized satisfactorily. The organicresin materials have generally a low dielectric constant, and theparasitic capacitance can be reduced. However, since they arehygroscopic, they are not suitable for the protective film. Therefore,the organic insulating material must be used in combination with thesilicon oxide film, the silicon oxynitride film or the silicon nitridefilm formed as the protective insulating film 750 as in this embodiment.

Thereafter, a resist mask having a predetermined pattern is formed byusing a photo-mask. Contact holes reaching the source or drain regionsof the respective island semiconductor layers are formed. The contactholes are formed by dry etching. In this case, a mixed gas of CF₄, O₂and He is used as the etching gas. The interlayer insulating film 751formed of the organic insulating material is first etched. Then, theetching gas is switched to CF₄ and O₂, and the protective insulatingfilm 750 is etched. To improve the selective ratio with the islandsemiconductor layers, the etching gas is switched further to CHF₃ andthe gate insulating film 725 is etched. In this way, the contact holescan be formed satisfactorily.

A conductive metal film is then formed by sputtering or vacuum vapordeposition, a resist mask is formed by a photo mask and source wirings752 to 756 and drain wirings 757 to 761 are formed by etching. The drainwiring 762 denotes a drain wiring of the adjoining pixel. Here, thedrain wiring 761 also functions as the pixel electrode. Though not shownin the figure, this electrode is formed from Ti film to a thicknessbetween 50 to 150 nm, contact is formed with the semiconductor filmwhich forms a source or drain region in the island semiconductor layer,and aluminum (Al) is formed to a thickness from 300 to 400 nm on the Tifilm, thereby forming a wiring.

FIG. 10E shows a top view of island semiconductor layers 715 and 716,gate electrodes 729 and 730, source wirings 752 and 753 and drainwirings 757 and 758 in this state. Source wirings 752 and 753 areconnected to the island semiconductor layers 715 and 716 through contactholes disposed in the interlayer insulating film (not shown) and theprotective insulating film at reference numerals 830 and 833. Further,drain wirings 757 and 758 are connected to the island semiconductorlayers 715 and 716 in 831 and 832.

Similarly FIG. 11E shows a top view of the island semiconductor layer719, the gate electrode 733, the capacitor wiring 734, the source wiring756 and the drain wiring 761 and the source wiring 756 is connected tothe island semiconductor layers 719 in the contact portion 834, and thedrain wiring 761, in the contact portion 835.

In any case, TFTs are formed by forming island semiconductor layers thathave the second shape by removing the areas where strain remains in anarea inside of the island semiconductor layers having the first shape.

When the hydrogenation treatment is conducted under this state,favorable results can be obtained for the improvement of TFTperformance. For example, the heat-treatment may be conducted preferablyat 300 to 450° C. for 1 to 12 hours in an atmosphere containing 3 to100% of hydrogen. A similar effect can be obtained by using the plasmahydrogenation method. Such a heat-treatment can diffuse hydrogenexisting in the protective insulating film 750 and the base film 702into the island semiconductor films 715 to 719 and can hydrogenate thesefilms. In any case, the defect density in the island semiconductorlayers 715 to 719 is lowered preferably to 10¹⁶/cm³ or below, and forthis purpose, hydrogen may be added in an amount of about 5×10¹⁸ to5×10¹⁹ atoms/cm³. (FIG. 9C)

Thus a substrate having the TFTs of the driving circuit and the pixelTFTs of the pixel portion over the same substrate can be completed. Thefirst p-channel TFT 800, the first n-channel TFT 801, the secondp-channel TFT 802 and the second n-channel TFT 803 are formed in thedriving circuit. The pixel TFT 804 and the storage capacitance 805 areformed in the pixel portion. In this specification, such a substratewill be referred to as an “active matrix substrate” for conveniencesake.

The first p-channel TFT 800 in the driving circuit has a single drainstructure that comprises in the island semiconductor film 715: thechannel formation region 806; and the source regions 807 a and 807 b andthe drain regions 808 a and 808 b each comprising the high concentrationp-type impurity region.

In the island semiconductor film 716 of the first n-channel TFT 801,there are formed: the channel formation region 809; the LDD region 810that overlaps the gate electrode 730; the source region 812; and thedrain region 811. In the LDD region, the length of this LDD region whichoverlaps the gate electrode 730 in the direction of the channel lengthis 0.5 to 3.0 μm, preferably 1.0 to 2.0 μm. As the length of the LDDregion in the n-channel TFT is determined in this way, a high electricfield occurring in the proximity of the drain region can be mitigated,and the occurrence of hot carriers and degradation of the TFT can beprevented.

The second p-channel TFT 802 of the driver circuit has the single drainstructure similarly in which the channel formation region 813, thesource regions 814 a and 814 b and the drain regions 815 a and 815 bcomprising the high concentration p-type impurity region are formed inthe island semiconductor film 717.

A channel formation region 816, LDD regions 817 and 818 which partiallyoverlap the gate electrode 732, a source region 820 and a drain region819 are formed in the island semiconductor film 718 of the secondn-channel TFT 803. The length of the LDD regions that overlap the gateelectrode 732 is also set at between 0.5 and 3.0 μm, preferably 1.0 to2.0 μm. Further, the length of the LDD regions that do not overlap thegate electrodes in the channel length direction is 0.5 to 4.0 μm,preferably 1.0 to 2.0 μm.

The channel forming regions 821 and 822, LDD regions 823 to 825, sourceor drain regions 826 to 828 are formed in the island semiconductor film719 of the pixel TFT 804. The length of the LDD region in the directionof the channel length is 0.5 to 4.0 μm, preferably 1.5 to 2.5 μm. Thestorage capacitance 805 is formed from the capacitor wiring 734, theinsulating film comprising the same material as the gate insulating filmand the semiconductor layer 829 that is connected to the drain region828 of the pixel TFT 804. In FIG. 9C, the pixel TFT 804 is a double gatestructure. However, it may have a single gate structure or a multi-gatestructure having a plurality of gate electrodes.

FIG. 12 is a top view showing almost one pixel of the pixel portion. Thecross section A-A′ in the drawing corresponds to the sectional view ofthe pixel portion shown in FIG. 9C. The gate electrode 733 of the pixelTFT 804 crosses the island semiconductor layer 719 below it through agate insulating film, not shown in the drawing. The source region, thedrain region and the LDD region are formed in the island semiconductorlayer, though they are not shown in the drawing. Reference numeral 834denotes a contact portion between the source wiring 756 and the sourceregion 826. Reference numeral 835 denotes a contact portion between thedrain wiring 761 and the drain region 828. A storage capacitance 805 isformed by the overlapping region of the semiconductor layer 829 thatextends from the drain region 828 of the pixel TFT 804 and a capacitancewiring 734 through the gate insulating film.

An active matrix substrate is completed as described above. The activematrix substrate manufactured in accordance with the present Embodimentarranges TFTs of appropriate structures corresponding to thespecifications of the pixel section and the driver circuit. By doing soit enables to improve operation performance and the reliability of theelectro-optical device which uses this active matrix substrate.

Note that in this Embodiment the drain wiring 761 of the pixel TFT 804is used as it is to the pixel electrode and has a structurecorresponding to a reflection type liquid crystal display device.However, the present invention can correspond to a transmission typeliquid crystal display device by forming a pixel electrode comprising atransparent conductive film which is electrically connected to the drainwiring 761.

Further, the present Embodiment is an example of manufacturing processof a semiconductor device using the present invention is not necessarilylimited to the material and the numerical value range shown in thisEmbodiment. Further, the arrangement of the LDD regions, etc., mayappropriately determined by the operator.

Embodiment 2

The example shown in Embodiment 1 is crystallization of an amorphoussemiconductor film by using the methods described in Embodiment Modes 1to 3 to perform laser annealing on the film. In the example, the laserannealing may be performed instead on a semiconductor film that has beencrystallized to a certain degree but not thoroughly.

That is, the laser annealing in accordance with the present invention isalso effective in the case where a crystalline semiconductor film thathas been crystallized by furnace annealing is further projected to laserannealing to enhance its crystallinity.

To be specific, the laser annealing method of Embodiment Modes 1 to 3may be used in the laser irradiation step described in Japanese PatentApplication Laid-open No. Hei 7-321339, Japanese Patent ApplicationLaid-open No. Hei 7-131034, and some other applications.

After the present invention is applied to the laser irradiation step ofthe above publications, a TFT using the crystalline semiconductor filmformed through that step may be formed. In other words, this embodimentcan be combined with Embodiment 1.

Embodiment 3

This embodiment gives a description of a process of manufacturing anactive matrix type liquid crystal display device using an active matrixsubstrate that is fabricated in accordance with Embodiments 1 and 2.First, as shown in FIG. 13A, spacers 901 a to 901 f are formed from aresin material by patterning on an active matrix substrate that is in astate illustrated in FIG. 9C. Alternatively, a known spherical silica orthe like may be dispersed and used as the spacer.

In this embodiment, as the spacers 901 a to 901 f made of a resinmaterial, NN 700 produced by JSR is applied by a spinner and is thenformed into a given pattern through exposure and development treatment.Further, it is heated in a clean oven or the like at a temperature of150 to 200° C. to cure. The thus formed spacers may vary in shapedepending on exposure conditions and development treatment conditions. Apreferable shape for the spacers is a column with flat top, because itensures the mechanical strength as a liquid crystal display panel whenthe active matrix substrate is bonded to an opposite substrate.

There is no particular limitation on the shape of the spacers and theymay take a conical shape, a pyramidal shape, etc. When a conical shapeis adopted, for example, specific dimensions of the spacers will be asfollows: a height H of 1.2 to 5 μm, a mean radius L1 of 5 to 7 μm, andthe ratio between the mean radius L1 and a radius L2 of 1 to 1.5, with ataper angle of ±15° or less on their sides.

Any arrangement may be taken for the spacers 901 a to 901 f. A preferredarrangement is as shown in FIG. 13A, in which the spacers are formed tooverlap and cover the contact portion 835 of the drain wiring 761 (pixelelectrode) in the pixel portion. Otherwise, the levelness is lost at thecontact portion 835 to fail to orientate liquid crystal there properly.By filling the contact portion 835 with the resin for the spacer,discrimination or the like can be prevented.

An orientation film 902 is then formed. Usually, polyimide resin is usedfor an orientation film of a liquid crystal display element. Afterforming the orientation film, rubbing treatment is performed so thatliquid crystal molecules are orientated with a certain pretilt angle. Itis preferable that a region that has not received the rubbing treatmentextends equal to or less than 2 μm in the rubbing direction from theends of the spacers 901 a to 901 f provided in the pixel portion. Inrubbing treatment, static electricity generated often causes trouble. Ifthe spacers 901 a to 901 f are formed to the extent to cover, at least,the source wiring and the drain wiring on the TFT of the driver circuit,they not only serve their original role as a spacer but also protect theTFT from static electricity in the rubbing process.

A light shielding film 904, an opposite electrode 905 made of atransparent conductive film, and an orientation film 906 are formed onan opposite substrate 903. As the light shielding film 904, a Ti, Cr, orAl film is formed to a thickness of 150 to 300 nm. The oppositesubstrate is then bonded, with a sealing material 907, to the activematrix substrate that has the pixel portion and the driver circuitformed thereon. A filler 908 is mixed in the sealing material 907, andthe filler 908 together with the spacers 901 a to 901 f bonds theopposite substrate and the active matrix substrate with a uniform gaptherebetween.

Then a liquid crystal material 909 is injected between the substrates,which are sealed completely with an end-sealing material (not shown). Aknown liquid crystal material may be used as the liquid crystal material909. For instance, a material that may be used other than a TN liquidcrystal is a thresholdless antiferroelectric mixed liquid crystalexhibiting an electro-optical response with which transmittance variescontinuously with respect to the electric field. Some thresholdlessantiferroelectric mixed liquid crystal show an electro-optical responsethat forms a shape of letter V when graphed. For details thereof, see“Characteristics and Driving Scheme of Polymer-stabilized MonostableFLCD Exhibiting Fast Response Time and High Contrast Ratio withGray-scale Capability”, H. Furue et al., SID, 1998, “A Full-colorThresholdless Antiferroelectric LCD Exhibiting Wide Viewing Angle withFast Response Time”. T. Yoshida et al., 841, SID '97 DIGEST, 1997,“Thresholdless Antiferroelectricity in Liquid Crystals and ItsApplication to Displays, S. Inui et al., 671–673, J. Mater. Chem. 6 (4),1996, and U.S. Pat. No. 5,594,569.

The active matrix type liquid crystal display device shown in FIG. 13Bis thus completed. Although the spacers 901 a to 901 e are formedseparately on at least the source wiring and the drain wiring on the TFTof the driver circuit in FIGS. 13A and 13B, the spacers may instead beformed to cover the entire surface of the driver circuit.

FIG. 14 is a top view of an active matrix substrate, showing thepositional relation of a pixel portion and a driver circuit portion to aspacer and a sealing material. A scanning signal driver circuit 1401 andan image signal driver circuit 1402 are provided as driver circuits inthe periphery of a pixel portion 1400. A signal processing circuit 1403such as a CPU and a memory may or may not be added thereto.

These driver circuits are connected to external input/output terminal1410 via a connecting wiring 1411. In the pixel portion 1400, a gatewiring group 1404 extending from the scanning signal driver circuit 1401and a source wiring group 1405 extending from the image signal drivercircuit 1402 intersect like a matrix to form pixels. Each of the pixelsis provided with a pixel TFT 804 and a capacitor storage 805.

The spacer 1406 provided in the pixel portion corresponds to the spacer901 f, and may be provided for every pixel. Alternatively, one spacermay be provided for every several pixels or for every several tenspixels arranged in matrix. That is, the ratio of the spacers to thetotal of the pixels is appropriately 20 to 100%. Spacers 1407 to 1409provided in the driver circuit portion may cover the entire surfacethereof, or may be separated into plural pieces to coincide with theposition of the source wiring and the drain wiring of each TFT as shownin FIGS. 13A and 13B.

The sealing material 907 is formed outside the pixel portion 1400, thescanning signal control circuit 1401, the image signal control circuit1402, and other signal processing circuit 1403, which are all on asubstrate 701, and inside the external input/output terminal 1410.

The structure of such an active matrix type liquid crystal display isdescribed with reference to a perspective view of FIG. 15. In FIG. 15,the active matrix substrate is comprised of the pixel portion 1400, thescanning signal driver circuit 1401, the image signal driver circuit1402, and other signal processing circuit 1403 which are formed on theglass substrate 701.

The pixel portion 1400 is provided with the pixel TFT 804 and thecapacitor storage 805, and the driver circuits provided in the peripheryof the pixel portion are constructed based on a CMOS circuit. Thescanning signal driver circuit 1401 and the image signal driver circuit1402 are connected to the pixel TFT 804 through a gate wiring 733 and asource wiring 756, respectively. A flexible printed circuit 1413 isconnected to the external input/output terminal 1410 with the intentionof using it to input an image signal or the like. The flexible printedcircuit (FPC) 1413 is fixed with a reinforced resin 1412 with anenhanced adhesion strength. The FPC is connected to each driver circuitvia the connecting wiring 1411. Though not shown in the drawing, anopposite substrate 903 is provided with a light shielding film and atransparent electrode.

The liquid crystal display device having the structure as such can befabricated using an active matrix substrate shown in Embodiments 1 and2. Employing an active matrix substrate shown in FIG. 9C, for instance,a reflection type liquid crystal display device is obtained, while atransmission type liquid crystal display device is obtained whenemploying an active matrix substrate that uses a transparent conductivefilm for a pixel electrode as shown in Embodiment 1.

Embodiment 4

Although Embodiments 1 to 3 show examples where the present invention isapplied to a liquid crystal display device, the invention is applicableto any semiconductor device as long as it uses a TFT.

Specifically, the present invention can be implemented in laserannealing step of a semiconductor film in manufacturing an active matrixtype EL (electroluminescence) display device or an active matrix type EC(electrochromics) display device. In that case, any of the structures ofEmbodiment Modes 1 to 3 may be employed.

The present invention is an invention pertaining to the laser annealingstep out of a manufacturing process of a TFT, and known procedures maybe applied to the rest of the steps of the manufacturing process.Therefore, the present invention is applied to known techniques whenmanufacturing an active matrix type EL display device or an activematrix type EC display device. To fabricate these display devicesreferring to the manufacturing process illustrated in FIGS. 7A to 9C isalso possible, of course.

Embodiment 5

The present invention can be embodied for an electronic device (alsocalled electronic equipment) having an electro-optical device such as anactive matrix type liquid crystal display device or an active matrixtype EL as its display. As the electronic device, a personal computer, adigital camera, a video camera, a portable information terminal (such asa mobile computer, a cellular phone, and an electronic book) anavigation system, etc. can be named.

FIG. 16A shows a personal computer that is comprised of a main body 2001provided with a micro processor, a memory, etc., an image input unit2002, a display unit 2003, and a keyboard 2004. The present inventioncan be implemented in fabricating the display unit 2003 and other signalprocessing circuits.

FIG. 16B shows a video camera that is comprised of a main body 2101, adisplay unit 2102, an audio input unit 2103, operation switches 2104, abattery 2105, and an image receiving unit 2106. The present inventioncan be implemented in fabricating the display unit 2102 and other drivercircuits.

FIG. 16C shows a goggle type display that is comprised of a main body2201, display units 2202, and arm portions 2203. The present inventioncan be implemented in fabricating the display units 2202 and othernot-shown driver circuits.

FIG. 16D shows an electronic game machine that is comprised of a mainbody 2301 loaded with an electric circuit 2308 such as a CPU and with arecording medium 2304, a controller 2305, a display unit 2303, and adisplay unit 2302 incorporated in the main body 2301. The display unit2303 and the display unit 2302 incorporated in the main body 2301 maydisplay the same information. Alternatively, the former may serve as amain display unit while the latter serve as a sub-display unit todisplay information of the recording medium 2304 or the operation statusof the machine. The latter may instead serve as an operating panel byadding thereto the touch sensor function. The main body 2301, thecontroller 2305 and the display unit 2303 transmit signals to oneanother through wired communication, or through wireless communicationor optical communication by providing sensor units 2306, 2307. Thepresent invention can be implemented in fabricating the display units2302, 2303. A conventional CRT display may be used as the display unit2303.

FIG. 16E shows a player which uses a recording medium in which a programis stored (hereinafter referred to as a recording medium) and which iscomprised of a main body 2401, a display unit 2402, speaker units 2403,a recording medium 2404, and operation switches 2405. A DVD (DigitalVersatile Disc), a compact disc (CD) or the like is used as therecording medium to enable the player to reproduce a music program,display an image, play a video game (or a television game), or displayinformation obtained through the Internet. The present invention can beimplemented in fabricating the display unit 2402 and other drivercircuits.

FIG. 16F shows a digital camera that is comprised of a main body 2501, adisplay unit 2502, an eye-piece portion 2503, operation switches 2504,and an image receiving unit (not shown). The present invention can beimplemented in fabricating the display unit 2502 and other drivercircuits.

FIG. 17A shows a front type projector that is comprised of a lightsource optical system and display device 2601, and a screen 2602. Thepresent invention can be implemented in fabricating the display deviceand other driver circuits. FIG. 17B shows a rear type projector that iscomprised of a main body 2701, a light source optical system and displaydevice 2702, a mirror 2703, and a screen 2704. The present invention canbe implemented in fabricating the display device and other drivercircuits.

Illustrated in FIG. 17C is an example of the structure of the lightsource optical system and display devices 2601, 2702 that are shown inFIGS. 17A and 17B, respectively. Each of the light source optical systemand display devices 2601, 2702 is comprised of a light source opticalsystem 2801, mirrors 2802, 2804 to 2806, dichroic mirrors 2803, a beamsplitter 2807, liquid crystal display devices 2808, phase differenceplates 2809, and a projection optical system 2810. The projectionoptical system 2810 is made up of a plurality of optical lenses.

FIG. 17C shows a three panel type where three liquid crystal displaydevices 2808 are used. However, the light source optical system anddisplay devices are not limited to this type and may be composed of asingle panel type optical system. A light path indicated by the arrow inFIG. 17C may suitably be provided with an optical lens, a film having apolarizing function, a film for adjusting the phase, an IR film, etc.

Illustrated in FIG. 17D is an example of the structure of the lightsource optical system 2801 that is shown in FIG. 17C. In thisembodiment, the light source optical system 2801 is comprised of areflector 2811, a light source 2812, lens arrays 2813, 2814, apolarization converting element 2815, and a condenser lens 2816. Notethat the light source optical system shown in FIG. 17D is an example andthe system 2801 is not limited to the illustrated structure.

Although not shown in here, the present invention may be implemented inmanufacturing a navigation system, a reading circuit for an imagesensor, etc., in addition to those applications illustrated in theabove. The application range of the present invention is thus so widethat the invention can be implemented in manufacturing electronicdevices of any field.

Embodiment 6

In contrast to Embodiment 1 where the methods of Embodiment Modes 1 to 3are used after patterning, this embodiment shows an example withreference to FIG. 18 in which irradiation with laser light is carriedout using the method of Embodiment Mode 1 before the patterning.

First, a state shown in FIG. 7A is obtained in accordance withEmbodiment 1.

A step of crystallizing the semiconductor film is then conducted. Adescription will be given below on the crystallization step employed inthis embodiment, i.e., irradiating the front side and the back side ofthe semiconductor film with laser light, which is illustrated in FIG.18.

In FIG. 18, reference symbol 1801 denotes a light transmittablesubstrate with an insulating film 1802 and an amorphous semiconductorfilm (or a microcrystal semiconductor film) 1803 formed on its frontside. A reflective member 1804 for reflecting laser light is arrangedbeneath the light transmittable substrate 1801.

The light transmittable substrate 1801 may be a glass substrate, aquartz substrate, a crystallized glass substrate or a plastic substrate.The light transmittable substrate 1801 by itself can adjust theeffective energy intensity of a secondary laser light. For theinsulating film 1802, an insulating film containing silicon, such as asilicon oxide film or a silicon oxide nitride film (SiOxNy) film, may beused. The adjustment of the effective energy intensity of the secondarylaser light may be made by the insulating film 1802 instead.

In the structure of FIG. 18, the secondary laser light is a laser lightthat passed through the amorphous semiconductor film 1803 once and thenreflected at the reflective member 1804. Accordingly, it is alsopossible to adjust the effective energy intensity of the secondary laserlight by the amorphous semiconductor film 1803. Examples of theamorphous semiconductor film 1803 include a compound semiconductor filmsuch as an amorphous silicon germanium film, other than an amorphoussilicon film.

A metal film formed on a surface (where the laser light is to bereflected) of a substrate may be used as the reflective member 1804.Alternatively, a substrate formed of an metal element may serve as thereflective member 1804. In that case, any material may be used for themetal film. Typically used is a metal film containing any element chosenout of silicon (Si), aluminum (Al), silver (Ag), tungsten (W), titanium(Ti), and tantalum (Ta). For example, titanium nitride or tantalumnitride (TaN) may be used.

The reflective member 1804 may be provided in contact with the lighttransmittable substrate 1801, or spaced apart therefrom. It is alsopossible to directly form a metal film as above on the back side(opposite side of the front side) of the substrate 1801, instead ofarranging the reflective member 1804, so that the laser light isreflected at the metal film. In either way, the effective energyintensity of the secondary laser light can be adjusted by changing thereflectance of the reflective member 1804. If the reflective member 1804is placed apart from the light transmittable substrate 1801, it is alsopossible to adjust the effective energy intensity of the secondary laserlight by gas charged in a gap between the reflective member and thesubstrate.

The amorphous semiconductor film 1803 is then irradiated with the laserlight that has been linearized through the optical system 201 (only thecylindrical lens 207 is shown in the drawing) illustrated in FIGS. 2Aand 2B. The irradiation with the linearized laser light is made byscanning the laser light.

The important thing, in any case, is that the effective energy intensityratio (I₀′/I₀) between a primary laser light 1805, which passes throughthe cylindrical lens 207 to be used to irradiate the front side of theamorphous semiconductor film 1803, and a secondary laser light 1806,which passes through the amorphous semiconductor film 1803 and isreflected once at the reflective member 1804 to be used to irradiatedthe back side of the amorphous semiconductor film 1803, satisfies therelation of 0<I₀′I₀<1, or 1<I₀′/I₀. To achieve this, the reflectance ofthe reflective member 1804 to the laser light is preferably 20 to 80%.At this point, some of the measures for attenuating the effective energyintensity of the secondary laser light, which have been mentioned abovein this embodiment, may be combined to obtain the desired intensityratio.

The laser light passes through the cylindrical lens 207 to have an angleof incident of 45 to 90° with respect to the front side of the substrateduring the process of being condensed. For that reason, the secondarylaser light 1806 reaches further to the back side of the amorphoussemiconductor film 1803 so as to irradiate there. The secondary laserlight 1806 may be obtained more efficiently by forming an uneven portionon the reflective surface of the reflective member 1804 to diffuse thelaser light.

An appropriate laser light is the one with its wavelength set within awavelength range (around 530 nm) in which the light transmissioncomponent and the light absorption component with respect to theamorphous semiconductor film 1803 are sufficient. In this embodiment,the crystallization is made by the second harmonic (wavelength, 532 nm)of a YAG laser.

Using the second harmonic, a part of the irradiated light transmitsthrough the amorphous semiconductor film and is reflected by thereflective member so that the back side of the amorphous semiconductorfilm is irradiated. Therefore, the secondary laser light 1806 can beobtained efficiently.

The obtained semiconductor film is next patterned to gain an island-likesemiconductor film.

The rest of the steps are carried out in accordance with Embodiment 1 toobtain an active matrix substrate.

This embodiment may also be combined with Embodiment 2. If Embodiment 3is used with this embodiment, then an active matrix type liquid crystaldisplay device is obtained. Moreover, this embodiment may be applied tothe semiconductor devices shown in Embodiments 4 and 5.

According to the present invention, improvement of the throughput fromthe laser annealing that uses a conventional excimer laser can beachieved by employing a solid state laser that is easy to maintain, aswell as the throughput is improved by linearizing the laser light inlaser annealing. This leads to reduction in production cost of a TFT anda semiconductor device formed from the TFT, such as a liquid crystaldisplay device.

Moreover, to conduct laser annealing by irradiating both the front sideand the back side of the amorphous semiconductor film with laser lightmakes it possible to obtain a crystalline semiconductor film with alarger crystal grain size as compared to prior art (where only the frontside of the amorphous semiconductor film is irradiated with laserlight). The obtainment of the crystalline semiconductor film with alarger crystal grain size further can lead to a great improvement of theability of a semiconductor device.

1. A method of manufacturing a semiconductor device comprising the stepsof: forming a semiconductor film over a substrate; crystallizing thesemiconductor film by irradiation of the second harmonic of a YVO₄laser; and patterning the crystallized semiconductor film to form asemiconductor island.
 2. A method according to claim 1, wherein thesemiconductor film is an amorphous semiconductor film.
 3. A methodaccording to claim 1, wherein the semiconductor film is a micro crystalsemiconductor film.
 4. A method according to claim 1, wherein the YVO₄laser is an Nd: YVO₄ laser.
 5. A method according to claim 1, whereinthe YVO₄ laser has an oblong shape.
 6. A method according to claim 1,wherein the YVO₄ laser has an aspect ratio of 100 to
 10000. 7. A methodaccording to claim 1, wherein the semiconductor film comprises silicongermanium.
 8. A method according to claim 1, further comprising stepsof: forming a gate electrode over the semiconductor island, wherein thesemiconductor island includes at least a channel formation region.
 9. Amethod of manufacturing a semiconductor device comprising the steps of:forming a semiconductor film over a substrate; crystallizing thesemiconductor film by irradiation of the second harmonic of a YVO₄ laserhaving a linear shape; and patterning the crystallized semiconductorfilm to form a semiconductor island.
 10. A method according to claim 9,wherein the semiconductor film is an amorphous semiconductor film.
 11. Amethod according to claim 9, wherein the semiconductor film is a microcrystal semiconductor film.
 12. A method according to claim 9, whereinthe YVO₄ laser is an Nd: YVO₄ laser.
 13. A method according to claim 9,wherein the YVO₄ laser has an aspect ratio of 100 to
 10000. 14. A methodaccording to claim 9, wherein the semiconductor film comprises silicongermanium.
 15. A method according to claim 9, further comprising stepsof: forming a gate electrode over the semiconductor island, wherein thesemiconductor island includes at least a channel formation region.
 16. Amethod of manufacturing a semiconductor device comprising the steps of:forming a semiconductor film over a substrate; patterning thesemiconductor film to form a semiconductor island; and crystallizing thesemiconductor island by irradiation of the second harmonic of a YVO₄laser.
 17. A method according to claim 16, wherein the semiconductorfilm is an amorphous semiconductor film.
 18. A method according to claim16, wherein the semiconductor film is a micro crystal semiconductorfilm.
 19. A method according to claim 16, wherein the YVO₄ laser is anNd: YVO₄ laser.
 20. A method according to claim 16, wherein thesemiconductor film comprises silicon germanium.
 21. A method accordingto claim 16, further comprising steps of: forming a gate electrode overthe semiconductor island, wherein the semiconductor island includes atleast a channel formation region.
 22. A method of manufacturing asemiconductor device comprising the steps of: forming a semiconductorfilm over a substrate; patterning the semiconductor film to form asemiconductor island; and crystallizing the semiconductor island byirradiation of the second harmonic of a YVO₄ laser having a linearshape.
 23. A method according to claim 22, wherein the semiconductorfilm is an amorphous semiconductor film.
 24. A method according to claim22, wherein the semiconductor film is a micro crystal semiconductorfilm.
 25. A method according to claim 22, wherein the YVO₄ laser has anoblong shape.
 26. A method according to claim 22, wherein the YVO₄ laserhas an aspect ratio of 100 to
 10000. 27. A method according to claim 22,wherein the semiconductor film comprises silicon germanium.
 28. A methodaccording to claim 22, further comprising steps of: forming a gateelectrode over the semiconductor island, wherein the semiconductorisland includes at least a channel formation region.
 29. A methodaccording to claim 22, wherein the YVO₄ laser is an Nd: YVO₄ laser. 30.A method of manufacturing a semiconductor device comprising the stepsof: forming a semiconductor film over a substrate; crystallizing thesemiconductor film by irradiation of the second harmonic of a YVO₄laser; and patterning the crystallized semiconductor film to form asemiconductor island, wherein the second harmonic of the YVO4 laser hasa shape at an irradiation surface which has aspect ratio of 10 or more.31. A method according to claim 30, wherein the semiconductor film is anamorphous semiconductor film.
 32. A method according to claim 30,wherein the semiconductor film is a micro crystal semiconductor film.33. A method according to claim 30, wherein the YVO₄ laser is an Nd:YVO₄ laser.
 34. A method according to claim 30, wherein the YVO₄ laserhas an oblong shape.
 35. A method according to claim 30, wherein theYVO₄ laser has an aspect ratio of 100 to
 10000. 36. A method accordingto claim 30, wherein the semiconductor film comprises silicon germanium.37. A method according to claim 30, further comprising steps of: forminga gate electrode over the semiconductor island, wherein thesemiconductor island includes at least a channel formation region.
 38. Amethod for manufacturing a semiconductor device comprising the steps of:forming an insulating film over a substrate; forming a semiconductorfilm on the insulating film; crystallizing the semiconductor film byirradiation of the second harmonic of a YVO₄ laser; and patterning thecrystallized semiconductor film to form a semiconductor island, whereinthe insulating film comprises at least one material selected from thegroup consisting of silicon oxide, silicon oxynitride and siliconnitride.
 39. A method according to claim 38, wherein the semiconductorfilm is an amorphous semiconductor film.
 40. A method according to claim38, wherein the semiconductor film is a micro crystal semiconductorfilm.
 41. A method according to claim 38, wherein the YVO₄ laser is anNd: YVO₄ laser.
 42. A method according to claim 38, wherein the YVO₄laser has an oblong shape.
 43. A method according to claim 38, whereinthe YVO₄ laser has an aspect ratio of 100 to
 10000. 44. A methodaccording to claim 38, wherein the semiconductor film comprises silicongermanium.
 45. A method according to claim 38, further comprising stepsof: forming a gate electrode over the semiconductor island, wherein thesemiconductor island includes at least a channel formation region.